Over the years, there have been a number of really nice sounding 6V6 amplifiers that were on the market. In fact, I've got an old Harmon Kardon 6V6 integrated sitting on my shelf waiting for me to find the time to bring it back to life. In addition to Harmon and smaller amp manufacturers like Bell and Stromberg Carlson, there were a number of organ manufacturers that used the 6V6 as the basis of design. I've seen Hammond, Magnavox, RCA not to mention some of the guitar amps like Fender, and the vintage Supro and Silvertone that use the 6V6 as their basis of design. One of the more interesting uses of the 6V6 in amplification I've seen was by Baldwin. They used a 6V6 to drive a field coil speaker. And then there is the truly legendary Leslie amplifier used behind the Hammond B-3 organ. Several of the Leslie designs used 6V6's.
I find it rather interesting that more manufacturers haven't used the 6v6 more often. Sure, even in push pull configuration it only puts out about 10 watts but there are way more than a few speakers that this design could mate very well with.
The driver tube chosen for this design is the 6u8. This is an interesting choice as opposed to the typical 12A series of driver tubes, which are double triodes; the 6U8 is a combination Triode and pentode. The 6U8 has a gain (Gm) of 5200 in the pentode side and 8500 on the triode side. It was originally designed as an oscillator or a pentode mixer in FM and TV receivers. Here, Quest For Sound is using the triode side to amplify the incoming signal while the pentode is being used to split the phase and drive the 6V6. This choice in driver tube works just fine, it is just a slightly different design than is prevalent in today's market.
There aren't many modern commercial offerings that come to mind that use the 6U8 as a driver tube. The only ones I can remember are from the past. Stromberg Carlson used the 6U8 in a few designs, as did Magnavox. The 6U8 was used fairly regularly in tuners, short wave, Ham radios and televisions as an oscillator. I know my vintage HH Scott 330 tuner has one or two in it. With a tube this common to the industry, that means there are tons of them out there that can be had (usually) cheap. Lets not forget that the Chinese are still producing new stock of this tube.
The coupling caps used in the SQ-84 are the Nichicon XK Metalized Polyester films (.22uF if you are interested). The resistors used appear to be metal oxides (pretty much) throughout. The tube bases are of the nice ceramic variety. The internal wiring appears to be copper and is neatly routed. One thing to note, the internal wiring is all point-to-point with the exception of the power supply module. The SQ-84 uses a few terminal blocks for the coupling caps and what appear to be the (self) biasing resistors (I didn't spend enough time inside to do a complete reverse engineering job).
The housing to the amplifier is a nice heavy gauge steel, with the corners continuously welded rather than lapped and tack welded. That is a very nice attention to detail. The front faceplate is a 0.5-inch thick piece of finished white wood. Also on the front you will find a large, easy to spin volume knob. Besides the power switch on the front there is also a 0.25-inch TRS jack and switch so that you can throw the SQ-84 into headphone mode, thus turning off the speakers. No worries about toasting your output trannies as the headphones provide the required load to protect the amplifier.
On the bottom is a simple, vented, metal plate and four chromed feet with rubber isolators. On the back you'll find your usual fare of binding posts, a single pair of input RCA jacks and an IEC female for line voltage. Although this unit comes with a tube cage that encompasses the entire top of the amp, I preferred its looks and sound with it off exposing the tubes and transformers. True, she's got that high school science project look to her since the transformers and choke are unpotted, but that is right up my geek alley.
When it comes to the 6V6 tubes, that one is a slightly different story. I've got a number of 6V6 tubes I've collected over the years. What I finally I settled on were a pair of Ken-Rad's mated with a pair of RCA's. This rather odd pairing produced the most even presentation top to bottom.
As for the Chinese tubes, they aren't too bad sounding, just a bit thin in the midrange and a tad hard on the top. That's completely OK. Know why? NOS 6V6's on eBay are dirt-cheap. You can pick up an NOS quad of nearly whatever brand you want for around fifty clams. Same goes for the 6U8, a nice NOS pair sells for under $20. Think about I, that is cheaper than a single 12AX7 Telefunken smooth plate. So needless to say, I spent the rest of my listening time using my NOS 6V6's running in place of the stock tubes.
The Blue Room
After plugging the SQ-84 into the 16-Ohm Goodman's, I found that the bass was tight and tuneful. The first I started with was one of my faves, "Throwdown at the Hoedown" from Left of Cool byBéla Fleck & The Flecktones. Here I found the bass quite good. Between Victor Wooten's finger gymnastics on the bass and Futureman's (Victor's brother) SynthAxe Drumitar there is enough complex bass passages on this track to trip up nearly any amplifier. As I listened intently, I didn't notice any loss of control or overhang at all. The SQ-84 performed quite well, maintaining good pace and rhythm, never showing hints of sounding slow.
Next up was Bach "Toccata and Fugue in D Minor" from Organ and Choir at the Christ Church Cathedral by Dennis Bergin. I used this track to check for bass extension. This particular recording is absolutely brutal on amps and speakers. As I listened, the SQ-84 faired pretty well. The SQ084 struggled a bit reproducing the lowest half octave of bass but it never sounded loose or flabby. Just to make sure my ears weren't deceiving me, I double-checked this with my Sencore SP295. My meter confirmed what I was hearing.
After an extended stay with the Goodman's, I decided to give the SQ-84 a break from driving bass. I reassembled my main reference system placing the SQ-84 in space where my Welborne DRD's typically reside and let it drive my Lowthers from 150Hz and up. Sure, this tells me zip about bass response and speaker interaction but it whispers volumes about the true character of the amp. Mainly, low level resolution and detail retrieval. I'll also pick up major hints about the SQ-84's ability to convey special cues regarding soundstaging and all its nuances.
As I listened to Roy Hardgrove's latest release, Nothing Serious, he and Slide Hampton pair up to play some amazing Jazz, The SQ-84 shows off that lush and full sound of the 6V6 tube that I've experienced a number of times before. The 6V6 in this circuit gives a marvelous texture to Slide Hampton's trombone. His trombone takes on a rich, buttery sound quality, just as it should. Though not the most refined amp I've heard, driving my Lowther PM2A loudspeakers, it most certainly takes that edge off some of the more aggressive CDs I own allowing me to absolutely get lost in the music. And after all, isn't that exactly what we really want to do, get lost in the music?
When it comes to the extension of the SQ-84, each of the tracks I chose sounded quite good. There was ample air being projected within the sonic picture. Gentle taps on the ride cymbals displayed a nice shimmer and definition though slightly muted. This was a more than welcome quality when I was playing some of my harsher recordings.
When it came to a few more of the audiophile qualities we look for in amplifiers, the SQ-84 faired quite well. Soundstaging was well on par with most amps out there. The images were ever so slightly larger than those of my SET's but their positioning was spot on. The width of stage was quite good too. Using my usual Pink Floyd's "Signs of Life" from Momentary Lapse of Reason the water lapping on the shore projected itself from about three to four feet outside of the speaker plane.
At this point the SQ-84 has me rethinking the use of those Nichicon coupling caps. At first, I sort of wrote them off as being a little less than audiophile grade capacitors, especially since they were in the coupling position. I'm used to seeing (and using) the best caps available in that position, especially since it's directly in the signal path. I have to say that I've used that same Nichicon cap a number of times as a bypass to a power supply. There I found it to work extremely well, so well that I have a rather large stock of them in my parts bins. Though not the most revealing of caps, the little Nichicon sure conveys plenty of emotion and a decent amount of detail. I could see using the Nichicon and bypassing it with a more revealing cap allowing the Nichicon to add some much needed emotion to few of the more sterile sounding coupling caps on the market. I may have to play with these in a future project somewhere down the road.
The presentation was fairly relaxed as it should have been since this is how these speakers are voiced. One thing the Bella's have is reasonably solid bass when paired with the proper tube amp. They are a sealed design and don't present an overly difficult load for tube amps.
When the SQ-84 was connected, I did notice that the bass was a bit loose when compared to my factory modified JoLida 102B. Guessing, this was likely due to the back feed from the Bella's at the drivers Fs. Remember, a speaker is a transformer that feeds back to your amplifier in the form of AC. This doesn't mean that the SQ-84 has weak bass; it just means that the two were likely not the best pairing.
When it came to the rest of the sound spectrum when playing on a full range speaker, the SQ-84 did a fine job. It has a very nice midrange bloom much like the EL84 amps. This bloom is not a negative attribute. It is part of what draws many of us into the music. For me, if you have a thin sounding midbass, the music becomes flat, dull and lifeless. That isn't the case with the SQ-84. She's got tons of life and is extremely seductive. Every piece of music that I used to gauge the midrange sounded absolutely lovely on the SQ-84. There is something about the design that is completely involving.
As I moved on up to the treble region, the SQ-84 remained relatively clean and showed nice extension. Overall, the treble was quite smooth never giving any hints of being harsh or grainy. In the end, the combination of the SQ-84 and the Response Audio Musica Bella's was a nice, musical combination. This pairing produced a very laid back presentation that was fun to listen to. There is a pretty strong likelihood that if you are a detail freak, you should probably think about a different pairing. The laid back nature of the SQ-84 would be better mated with a more forward sounding pair of speakers.
The Grape Room
The source I used was my trusty old AH! Njoe Tjoeb with the upsampler installed. With the SQ-84 being slightly relaxed sounding; I thought the upsampler would add some depth and detail to this combination and I was right. This brought forward a bit more detail to bring some balance to the sound. After a bit of fiddling with speaker placement, port plugs and some well placed additional room treatments, I finally found resting place for the Epiphany's where I was getting nice, even bass. I was a bit surprised that I needed to play with the speaker placement and treatments since with the Odyssey Etesian pre and Khartago amp that normally takes up residence in this room sounded extremely good as the system sat. With most of the amps that make a guest appearance in this room, I don't have to mess with the speaker placement but with the SQ-84 I did. The speakers found themselves sitting about 8" further out from the wall with a pair of 2' x 4' x 2" thick OC703 fiberglass panels directly behind them. Hmmmm, riddles…all the time riddles.
Once I finally settled in for some critical listening, I was immediately reminded of the rich tone that dominated the Lowthers when being driven by the SQ-84. While being rich and buttery, this little amp came across with ample detail that would keep most all music lovers very happy. The sound was big, bold and wide open, just as I expected from the Epiphany's. These little gems have never failed to project a much larger soundstage than your typical speaker. The SQ-84 was tossing out an image that extended a solid four to five feet beyond the boundaries if the speakers.
As I sat there listening to Graham Nash and David Crosby's latest release Highlights, this pair of old friends take up residence on the virtual soundstage a solid four or five feet behind the speakers. The SQ-84 did a fine job of placement and overall performer definition. Though not the sharpest image I've heard, it is quite good without being overstated.
Upper end extension and clarity was quite nice also. Though slightly subdued through the Epiphany's, none of the tracks I played ever left me wanting for more or better treble. There was ample air around the instruments and performers giving you those crucial spatial cues we all love so well.
Wanting to play with the SQ-84 some more, I decided to pull out my newly acquired pair of Aperion 632 monitors. Again, another seemingly tube friendly speaker rated at about 86dB. This difference between the Aperion and the Epiphany loudspeakers are the presentation. The Epiphany's are a ‘back hall' speaker where the Aperion's are a front hall speaker. Here I wanted to get an idea of how a more ‘defined' two way reacted with the SQ-84 amp.
Moving my listening position forward towards the speakers about an extra foot or two in my small room, brought me a to a new level of understanding about this amps voicing. The reason I had to move up a bit is because the Aperions provide a fair amount more (relative) bass than the Epiphany's plus they load the room differently.
As I listened to the Aperion's, the sound completely opened up and room became the hall. I played Pat Metheny's "Across The Sky" and then "Roots of Coincidence" both from Imaginary Day, the bass being delivered was thunderous, though showed some hints of being slightly under-damped. The Aperion's literally disappeared in this small room to be replaced only with Pat, Lyle and the boys. Again, the rich buttery tone of Pats guitar sounded quite exquisite as portrayed by the SQ-84.
Since Pat sounded so good, I decided to put on another of my favorite guitarists, the King of Tone, Eric Johnson. On this his latest release Bloom, are sixteen yummy tracks of tonal bliss, provided by the Master of Marshall (short stack) and a Stratocaster, something the SQ-84 should excel at. A quick push of the play button and it told me that the Sound Quest didn't disappoint.
The SQ-84 As A Headphone Amplifier
Currently my main setup consists of the Graham Slee Solo headphone amp and a pair of Grado SR-80's. Some people might scoff at the 80's but to my ear, they sound ‘right'. I've had some highly regarded cans through this place like the Sennheiser 650's that so many seem to adore. Don't get me wrong, I liked them but I thought they sounded bloated, even with the $3000 Maxed Out Headroom headphone amp. I did find that I enjoyed the Etymotic er5s's quite a bit. They sounded quite neutral (again) to my ears. In turn, I recently picked up a pair of Shure 210 in-ears that aren't half bad for the price.
I've also strapped Beyerdynamics on, several of the Senn's and many, many of the upper line Grado's but I still keep coming back to my old standby's, the 80's. They sound pretty darned good to me. I also have a pair of Grado SR-60's. So there you have it, I'm a cheap, but good sounding headphone fan, Stax be damned.
From the minute I strapped on my cans, I knew I was in for a real experience. Just as I had hoped, all of the SQ-84's glorious tone shone through into headphones. For it's shortcomings as a stand alone integrated, it clearly stands out as a very good headphone amp. Never sounding the least bit harsh or grainy, the SQ-84 delivers music with a sweet, rich character that you just can't get with solid-state gear. As much as I love my Slee Solo (and it is truly a fine can amp), it is outclassed by the SQ-84. The sheer musicality of the Sound Quest and its 6V6 tubes is some of the most involving sounds I've had the pleasure to hear from a headphone amp.
With my Grado SR-80's, the bass was firm and deep with no hints of being rolled off when it reaches the depths of sonics. The same held true with the uppermost octaves. Treble extension and clarity were quite good when I strapped on the Grado's. As I mentioned, the SQ-84's tone shines through even on the headphone tap. So it follows, what I am hearing is an extremely enjoyable, non-fatiguing sound. You will get ample detail but the resolution may not to satisfy the detail freaks out there.
I should mention here that I did play with several pairs of cans. Though I prefer the sound of the Grado SR-80's, I plugged in my new Shure in-ears and also a pair of Grado SR-60's, both of which are slightly tilted up (or bass lite, however you wish to look at it). When I had these plugged in I found that the smooth, relaxed and slightly heavy sound I experienced with the SR-80's now revealed more detail and less accentuated bass. Overall, this was a far more even presentation, in audiophile terms. These pairings completely changed the complexion of the SQ-84. I went from listening to a relatively relaxed sounding headphone amp to listening to a killer pairing of cans and amp. It's all about balance and synergy.
Another thing about the SQ-84 as a headphone amp, this thing will play as loud as you could possibly imagine without clipping. The way the headphone circuit is wired is the tap comes off the downstream side of transformer to drive the headphones. That means once you get past the dropping resistor, you are getting some serious wattage delivered to your head. With the SQ-84 driving the Grados, I could have easily played it so loud that my head imploded, especially with CDs like Mad At Gravity, a CD that begs to be played at full volume. Fortunately, I didn't succumb to the volume monster though I was really tempted a few times.
One thing I must mention, when I had the headphones on I did hear a slight bit of noise, a hum to be precise. As noted, I heard this earlier when I was driving my Lowthers. With the cans, the hum is very subdued and all but un-noticeable until the music stops, but it is there.
When it comes to the clarity of the amp, personally, I feel that is a non-issue. Reason being, it is obvious by Quest for Sounds choice in coupling capacitors that they voiced this for tone and pure enjoyment rather than following some audiophile protocol. That is perfectly fine in my book, in fact I applaud it.
In The End
If you decide to take the plunge, be sure you take into consideration mating the SQ-84 to the proper speakers and you will get some extremely sweet sounds from the pairing. Forward sounding, tube friendly speakers will be right at home with the Sound Quest giving you that much needed balance. This is one of those times where I really wish I had my 16 Ohm Altec A-7's up and running. I'd bet front loaded horns would sound great being driven by the Sound Quest.
As a pure headphone amp, the SQ-84 is quite good. With the right headphones, it is some of the best amplification I've heard to date. Again, though not the ‘cleanest' sound I've found on the market, it sure makes music better than many amps I've heard. It was considerably more inviting than the Maxed out Headroom Amp I lived with for some time. Best part is, it is one-third the price. So, for you music fans out there who have tube friendly speakers and also want headphone capability, you might find the SQ-84 to be the perfect little integrated amp for you.